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Message-ID: <89c9f27c-f539-ef75-dc67-bdb0a8480c4b@gmail.com>
Date:   Wed, 26 Jul 2023 21:47:03 +0800
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Subject: Re: [PATCH V3 5/9] x86/hyperv: Use vmmcall to implement Hyper-V
 hypercall in sev-snp enlightened guest
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
        "daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
        "arnd@arndb.de" <arnd@arndb.de>
Cc:     Tianyu Lan <Tianyu.Lan@microsoft.com>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>
References: <20230718032304.136888-1-ltykernel@gmail.com>
 <20230718032304.136888-6-ltykernel@gmail.com>
 <BYAPR21MB16882FAEDEFAED59208ED9E0D700A@BYAPR21MB1688.namprd21.prod.outlook.com>
From:   Tianyu Lan <ltykernel@gmail.com>
In-Reply-To: <BYAPR21MB16882FAEDEFAED59208ED9E0D700A@BYAPR21MB1688.namprd21.prod.outlook.com>
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On 7/26/2023 11:44 AM, Michael Kelley (LINUX) wrote:
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index 2fa38e9f6207..025eda129d99 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -64,12 +64,12 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
>>   	if (!hv_hypercall_pg)
>>   		return U64_MAX;
>>
>> -	__asm__ __volatile__("mov %4, %%r8\n"
>> -			     CALL_NOSPEC
>> +	__asm__ __volatile__("mov %[output], %%r8\n"
>> +			     ALTERNATIVE("vmmcall", CALL_NOSPEC, X86_FEATURE_SEV_ES)
> Since this code is for SEV-SNP, what's the thinking behind using
> X86_FEATURE_SEV_ES in the ALTERNATIVE statements?   Don't you need
> to use X86_FEATURE_SEV_SNP (which is being added in another patch set that
> Boris Petkov pointed out).

Hi Michael:
	Thanks for your review. The patch mentioned by Boris has not been 
merged and so still use X86_FEATURE_SEV_ES here. We may replace the 
feature flag with X86_FEATURE_SEV_SNP after it's upstreamed.

> 
> Also, does this patch depend on Peter Zijlstra's patch to support nested
> ALTERNATIVE statements?  If so, that needs to be called out, probably in
> the cover letter.  Peter's patch doesn't yet appear in linux-next.
> 

It may work without Peterz's patch. Please see 
https://lkml.org/lkml/2023/6/27/520.
Peterz's patch optimizes ALTERNATIVE_n implementation with nested 
expression.